readme file for code example

7/30/2019 Readme File for Code Example

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The FFT operation is performed on the input signal, in-place. This means that the output of the FFT resides in the

same RAM locations where the input signal used to reside. The FFT is performed in the following steps:

1. Initialization: Generate Twiddle Factor Coefficients and store them in X-RAM or alternately use twiddle factor

coefficients stored in Program Flash.

2. Scale the input signal to lie within the range [-0.5, +0.5]. For fixed point fractional input data, this translates to

input samples in the range [0xC000,0x3FFF]. The scaling is achieved by simply right-shifting the input samples by 1

bit, assuming the input samples lie in the fixed point range [0x8000,0x7FFF] or [-1,+1).

3. Convert the real input signal vector to a complex vector by placing zeros in every other location to signify a

complex input whose imaginary part is 0x0000.

4. Butterfly computation: This is achieved by performing a call to the FFTComplexIP() function.

5. Bit-Reversed Re-ordering: The output array is re-ordered to be in bit-reversed order of the addresses. This is

achieved by a function call to BitReverseComplex().

6. SquareMagnitude computation: We then need to compute the magnitude of each complex element in the outputvector, so that we can estimate the energy in each spectral component/frequency bin. This is achieved by a call to a

special C-callable routine, SquareMagnitudeCplx(), written in assembler language. This routine will be incorporated

into the DSP library in future revisions of the C30 toolsuite. At that time, you may remove the source file,

cplxsqrmag.s from the project and include the latest DSP library file, libdsp-coff.a.

7. Peak-picking: We then find the frequency component with the largest energy by using the VectorMax() routine in

the DSP library.

8. Frequency Calculation: The value of the spectral component with the highest energy, in Hz, is calculated by

multiplying the array index of the largest element in the output array with the spectral (bin) resolution ( = sampling

rate/FFT size).

2. Folder Contents:

-------------------

This folder contains the following sub-folders:


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a. gld

This folder contains the linker script file for the example project.

This file is used for building the project. This file was provided with

the MPLAB C30 v1.33 toolsuite.

b. h

This folder contains C header files useful in building this

project. Device register and bit definitions are provided in

the *.h file that follows the device name. These files were provided

with the MPLAB C30 v1.33 toolsuite.

c. hex

This folder contains three file types - coff, hex and map.

These are files generated by the MPLAB C30 toolsuite on build

operation performed within MPLAB IDE. The *.map file contains

details on memory allocation for various variables, constants

and dsPIC30F instructions specified in the source and library

code. The *.hex file contains a binary file that may be

programmed into the dsPIC30F device. The *.coff file contains

a binary file that is used by MPLAB IDE for simulation.

d. inc

This folder contains Assembler include files useful in building this

project. Device register and bit definitions are provided in

the *.inc file that follows the device name. These files were provided

with the MPLAB C30 v1.33 toolsuite.

e. lib

This folder contains library archive files, which are a

collection of precompiled object files. The file


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named "libpic30-coff.a" contains the C run-time start-up

library. These file were provided with the

MPLAB C30 v1.33 toolsuite.

f. src

This folder contains all the C and Assembler source files (*.c,

*.s) used in demonstrating the described example. This folder

also contains a sub-folder named "obj" that stores compiled

object files generated when the project is built.

g. dsPICworks

This folder contains files created by dsPIC Filter Design and

dsPICworks Data Analysis and Design Software. Input signal files,

output signal files and filter specifications have been provided

here.

3. Suggested Development Resources:

-----------------------------------

a. MPLAB IDE v7.21 or later

b. MPLAB C30 v1.33 or later

c. MPLAB ICD 2 R23 or later

d. dsPICDEM 1.1 Development Board (See below)

e. dsPIC30F6014A Digital Signal Controller Plug-In Module (See below)

4. Reconfiguring the project for a different dsPIC30F device:

-------------------------------------------------------------

The Project/Workspace can be easily reconfigured for any dsPIC30F device.

Please use the following general guidelines:

a. Change device selection within MPLAB IDE to a dsPIC30F device of

your choice by using the following menu option:


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MPLAB IDE>>Configure>>Select Device

b. Provide the correct device linker script and header file for your

device. Device linker scripts and header files are available in your

MPLAB C30 installation folder under:

Device Linker Script-

YourDrive:>Program Files\Microchip\MPLAB C30\support\gld

Device C Header file-

YourDrive:>Program Files\Microchip\MPLAB C30\support\h

Device ASM Include file-

YourDrive:>Program Files\Microchip\MPLAB C30\support\inc

c. Provide the appropriate path to your MPLAB C30 support file locations

using the menu option:

MPLAB IDE>>Project>>Build Options>>Project

d. Chose the development board applicable to your device. Some options

are provided below:

- dsPICDEM 2 Development Board supports:

30F2010, 30F2011, 30F2012, 30F3010, 30F3011, 30F3012, 30F3013,

30F3014, 30F4011, 30F4012, 30F4013

- dsPICDEM 1.1 Development Board supports:

30F5013, 30F6010, 30F6011, 30F6012, 30F6013, 30F6014,

30F6011A, 30F6012A, 30F6013A, 30F6014A

- dsPICDEM MC1 Development Board supports:

30F6010, 30F6010A, 30F5016

e. Re-build the MPLAB project using the menu option:


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MPLAB IDE>>Project>>Build All

f. Download the hex file into the device and run.

5. Reconfiguring the project for a different FFT Size:

-------------------------------------------------------------

The project has been configured for a 256-pt FFT to be performed on a 30F6014A device.

Perform the following steps in sequence to change the device and FFT size.

(i) Change device selection within MPLAB IDE to a dsPIC30F device of

your choice by using the following menu option:

MPLAB IDE>>Configure>>Select Device

(ii) Provide the correct device linker script and header file for your

device. Device linker scripts and header files are available in your

MPLAB C30 installation folder under:

Device Linker Script-

YourDrive:>Program Files\Microchip\MPLAB C30\support\gld

Device C Header file-

YourDrive:>Program Files\Microchip\MPLAB C30\support\h

Device ASM Include file-

YourDrive:>Program Files\Microchip\MPLAB C30\support\inc

(iii) In the file FFT.h, perform the following changes:

- Change FFT_BLOCK_LENGTH to either 64, 128, 256 or 512

- Correspondingly, change LOG2_BLOCK_LENGTH to either 6, 7, 8 or

9 respectively

- If you would like to store Twiddle Factors coefficients in RAM

instead of Program Memory comment out the line of code as shown:

"//#define FFTTWIDCOEFFS_IN_PROGMEM "


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(iv) This project uses an input squarewave signal provided as PCM

samples in the file, "inputsignal_square1khz.c" in the array named

"sigCmpx[]". This array should be of length, FFT_BLOCK_LENGTH and

type "fractcomplex". So, for a 64-pt FFT, it should contain only

64 data samples and padded initially with 64 zeroes. This array

stores the output of the complex FFT operation and eventually

stores the magnitudes of the frequency bins.

Modify this array to suit the FFT size you are using. In a real

application, your data will likely be input from a real-world

signal.

(v) Re-build the MPLAB project using the menu option:

MPLAB IDE>>Project>>Build All

(vi) Download the hex file into the device and run.

6. Revision History :

---------------------

09/30/2005 - Initial Release of the Code Example

01/05/2006 - Corrected cplxsqrmag.s

01/17/2006 - Added "5. Reconfiguring the project for a different FFT

Size:" in this readme file and corrected an extern

definition in the main_FFTExample.c file

/**********************************************************************

* 2005 Microchip Technology Inc.

*

* FileName: main_FFTExample.c


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* Dependencies: Header (.h) files if applicable, see below

* Processor: dsPIC30Fxxxx

* Compiler: MPLAB C30 v1.33.00 or higher

* IDE: MPLAB IDE v7.20.01 or later

* Dev. Board Used: dsPICDEM 1.1 Development Board

* Hardware Dependencies: None

*

* SOFTWARE LICENSE AGREEMENT:

* Microchip Technology Inc. (Microchip) licenses this software to you

* solely for use with Microchip dsPIC digital signal controller

* products. The software is owned by Microchip and is protected under

* applicable copyright laws. All rights reserved.

*

* SOFTWARE IS PROVIDED AS IS. MICROCHIP EXPRESSLY DISCLAIMS ANY

* WARRANTY OF ANY KIND, WHETHER EXPRESS OR IMPLIED, INCLUDING BUT NOT

* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A

* PARTICULAR PURPOSE, OR NON-INFRINGEMENT. IN NO EVENT SHALL MICROCHIP

* BE LIABLE FOR ANY INCIDENTAL, SPECIAL, INDIRECT OR CONSEQUENTIAL

* DAMAGES, LOST PROFITS OR LOST DATA, HARM TO YOUR EQUIPMENT, COST OF

* PROCUREMENT OF SUBSTITUTE GOODS, TECHNOLOGY OR SERVICES, ANY CLAIMS

* BY THIRD PARTIES (INCLUDING BUT NOT LIMITED TO ANY DEFENSE THEREOF),

* ANY CLAIMS FOR INDEMNITY OR CONTRIBUTION, OR OTHER SIMILAR COSTS.

*

* REVISION HISTORY:

*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

* Author Date Comments on this revision

*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

* HV 09/30/05 First release of source file

*

*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


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*

* ADDITIONAL NOTES:

*

*

**********************************************************************/

#include

#include

#include "fft.h"

/* Device configuration register macros for building the hex file */

_FOSC(CSW_FSCM_OFF & XT_PLL8); /* XT with 8xPLL oscillator, Failsafe clock off */

_FWDT(WDT_OFF); /* Watchdog timer disabled */

_FBORPOR(PBOR_OFF & MCLR_EN); /* Brown-out reset disabled, MCLR reset enabled */

_FGS(CODE_PROT_OFF); /* Code protect disabled */

/* Extern definitions */

extern fractcomplex sigCmpx[FFT_BLOCK_LENGTH] /* Typically, the input signal to an FFT */

__attribute__ ((section (".ydata, data, ymemory"), /* routine is a complex array containing samples */

aligned (FFT_BLOCK_LENGTH * 2 *2))); /* of an input signal. For this example, */

/* we will provide the input signal in an */

/* array declared in Y-data space. */

/* Global Definitions */

#ifndef FFTTWIDCOEFFS_IN_PROGMEM

fractcomplex twiddleFactors[FFT_BLOCK_LENGTH/2] /* Declare Twiddle Factor array in X-space*/

__attribute__ ((section (".xbss, bss, xmemory"), aligned (FFT_BLOCK_LENGTH*2)));

#else

extern const fractcomplex twiddleFactors[FFT_BLOCK_LENGTH/2] /* Twiddle Factor array in Program memory */

__attribute__ ((space(auto_psv), aligned (FFT_BLOCK_LENGTH*2)));

#endif


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int peakFrequencyBin = 0; /* Declare post-FFT variables to compute the */

unsigned long peakFrequency = 0; /* frequency of the largest spectral component */

int main(void)

{

int i = 0;

fractional *p_real = &sigCmpx[0].real ;

fractcomplex *p_cmpx = &sigCmpx[0] ;

#ifndef FFTTWIDCOEFFS_IN_PROGMEM /* Generate TwiddleFactor Coefficients */

TwidFactorInit (LOG2_BLOCK_LENGTH, &twiddleFactors[0], 0); /* We need to do this only once at start-up */

#endif

for ( i = 0; i < FFT_BLOCK_LENGTH; i++ )/* The FFT function requires input data */

{ /* to be in the fractional fixed-point range [-0.5, +0.5]*/

*p_real = *p_real >>1 ; /* So, we shift all data samples by 1 bit to the right. */

*p_real++; /* Should you desire to optimize this process, perform */

} /* data scaling when first obtaining the time samples */

/* Or within the BitReverseComplex function source code */

p_real = &sigCmpx[(FFT_BLOCK_LENGTH/2)-1].real ; /* Set up pointers to convert real array */

p_cmpx = &sigCmpx[FFT_BLOCK_LENGTH-1] ; /* to a complex array. The input array initially has all */

/* the real input samples followed by a series of zeros */

for ( i = FFT_BLOCK_LENGTH; i > 0; i-- ) /* Convert the Real input sample array */

{ /* to a Complex input sample array */

(*p_cmpx).real = (*p_real--); /* We will simpy zero out the imaginary */


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(*p_cmpx--).imag = 0x0000; /* part of each data sample */

}

/* Perform FFT operation */

#ifndef FFTTWIDCOEFFS_IN_PROGMEM

FFTComplexIP (LOG2_BLOCK_LENGTH, &sigCmpx[0], &twiddleFactors[0], COEFFS_IN_DATA);

#else

FFTComplexIP (LOG2_BLOCK_LENGTH, &sigCmpx[0], (fractcomplex *) __builtin_psvoffset(&twiddleFactors[0]), (int)

__builtin_psvpage(&twiddleFactors[0]));

#endif

/* Store output samples in bit-reversed order of their addresses */

BitReverseComplex (LOG2_BLOCK_LENGTH, &sigCmpx[0]);

/* Compute the square magnitude of the complex FFT output array so we have a Real output vetor */

SquareMagnitudeCplx(FFT_BLOCK_LENGTH, &sigCmpx[0], &sigCmpx[0].real);

/* Find the frequency Bin ( = index into the SigCmpx[] array) that has the largest energy*/

/* i.e., the largest spectral component */

VectorMax(FFT_BLOCK_LENGTH/2, &sigCmpx[0].real, &peakFrequencyBin);

/* Compute the frequency (in Hz) of the largest spectral component */

peakFrequency = peakFrequencyBin*(SAMPLING_RATE/FFT_BLOCK_LENGTH);

while (1); /* Place a breakpoint here and observe the watch window variables */

}

----------------------------------------------------------------------------------------

/* Constant Definitions */

#define FFT_BLOCK_LENGTH 256 /* = Number of frequency points in the FFT */


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#define LOG2_BLOCK_LENGTH 8 /* = Number of "Butterfly" Stages in FFT processing */

#define SAMPLING_RATE 10000 /* = Rate at which input signal was sampled */

/* SAMPLING_RATE is used to calculate the frequency*/

/* of the largest element in the FFT output vector*/

#define FFTTWIDCOEFFS_IN_PROGMEM /*

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